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The metal dust produced from polishing wheels at Kunshan Zhongrong Metal Products Co.’s factory was so intense it seeped through Lu Qingmei’s face mask and coated her nose and mouth. After two days, she quit.

“When you go onto the production floor, you’re covered in gray dust in less than half a day,” the 25-year-old said of her stint in February at the Chinese factory, which finishes rims that end up in vehicles made by General Motors Co. (GM) and other carmakers. “It was dirty and tiring to work there.”

The decision to quit may have saved her life. Last week, a fireball ripped through the workshop, killing at least 75 workers and injuring 185 in China’s deadliest industrial disaster in more than a year. Not everyone’s been identified, including Lu’s sister-in-law.

The blast -- state media said it was triggered by tiny aluminum and magnesium flakes that caught fire -- has prompted China to announce a nationwide overhaul of safety practices, and reignited concern about occupational hazards in the world’s second-largest economy. Combustible dust, which has long bedeviled factories worldwide, was cited in at least four previous explosions that killed 26 people at Chinese industrial sites since 2009.

“This was not a random accident,” said Li Qiang, the New York-based director of China Labor Watch, a workers’ advocacy group. “This was entirely preventable if they had adopted safety measures. Under these circumstances, where dust had been allowed to accumulate the way it had, this was a fire hazard waiting to happen.”

7:35 a.m.

More than half of the company’s 450 employees were at work when the explosion struck soon after 7:35 a.m. on Aug. 2. The blast was so powerful it blew the roof off the factory in Kunshan city, about 50 kilometers (31 miles) west of Shanghai.

An initial investigation found the Zhongrong plant had overcrowded production lines, facilities that failed to meet safety standards and lacked equipment to remove dust, according to the official Xinhua News Agency. Yang Dongliang, director of the State Administration of Work Safety, said the findings showed a “very serious dereliction of duty,” Xinhua reported.

The factory sold its products to Citic Dicastal Co., a global supplier to GM.

While Zhongrong was an indirect supplier, GM requires all its direct suppliers to source from companies meeting appropriate standards, GM President Dan Ammann said. It’s “too soon to tell” whether GM will change its safety monitoring standards for indirect suppliers, he said.

‘All black’

Yesterday, about 100 friends and family were in a large hall of the Kunshan Convention and Exhibition Center, waiting for any updates about unaccounted workers. Among the family members was Lu, whose husband’s sister worked at the factory and was missing.

“My husband has taken time off work and he’s not slept well,” said Lu, a native of Anhui province.

Another woman said her 38-year-old aunt often left the production line filthy with soot before she went missing after the blast.

“The dust would be in her nose, ears and nails,” said the woman, who asked to identified only by her family name Xu. “They were all black.”

Xu herself had worked at the factory, though in a different section of the plant, and quit after a year. Although she complained about the conditions, she said her supervisor’s response was, “If you don’t like it, you can work elsewhere.”

Combustible dust

Three calls to Kunshan Zhongrong went unanswered yesterday. A person who answered a number listed on Dicastal’s website referred queries to an Aug. 2 news release that said the company met all safety regulations and was reassessing its operations.

Jiangsu province, which includes Kunshan, suspended production yesterday for safety checks at all workshops that process magnesium and aluminum, according to statement posted on the website of the Work Safety Administration of Suzhou city, which administers the area.

Combustible dust has plagued factories outside of China, causing 281 incidents that resulted in 119 deaths between 1980 and 2005 in the U.S., according to study by Chemical Safety Board, which investigates industrial accidents.

Most organic material and metals are combustible if ground into small enough particles. When disturbed, dust gathered on floors and other surfaces in poorly ventilated areas can shoot into the air as a flammable cloud.

People light candles for victims of the Kunshan Zhongrong Metal Co. factory blast in Kunshan, China, on August 2, 2014.

Liu Kaiming, the Shenzhen-based director of the Institute of Contemporary Observation, a non-governmental organization that studies labor issues, said combustible dust was “easily rectifiable” with training, ventilation systems and alarms.

“There still isn’t enough emphasis on rigorous enforcement of regulations,” Liu said. “Even though local officials conduct inspections, they’re mostly just walking through the complex.”

The Kunshan blast was China’s deadliest workplace disaster since a fire at a Jilin poultry plant killed 120 people in June last year. In December, Premier Li Keqiang intensified efforts to improve workplace safety, after explosions at an underground oil pipeline owned by China Petroleum & Chemical Corp. (386) killed 62 in the eastern port city of Qingdao.

In Kunshan, family members focused on finding out whether their loved ones survived the blast. A 38-year-old man from Hubei province said he had been fired from his job driving a delivery truck because he had missed work looking for a sister and brother-and-law who worked at the factory.

“The worst thing is, I don’t even know if they’re injured or dead,” said the man, who declined to identify himself beyond the surname Zhu. “I don’t know anything and it’s been days.”